1. Field of the Invention
The present invention relates to the field of touch techniques, and in particular to a capacitive touch unit and a capacitive touch screen with capacitive touch unit.
2. The Related Arts
The touch display screen as an input medium is one of the simplest and most convenient modes for human-machine dialogue. Hence, the touch display screen is widely applied to various electronic products. Based on the operating theory and information transmission medium, the touch screen products care categorized into four types: infrared touch screen, capacitive touch screen, resistive touch screen and surface acoustic wave touch screen, wherein the capacitive touch screen becomes the main stream technology for touch screen due to the advantages of long life-span, high transmittance and supporting multi-touch.
The capacitive touch screens include the surface capacitive type and the projected capacitive type. The projected capacitive type can be divided into self-capacitance type and mutual capacitance type. The self-capacitance type is by using Indium tin oxide (ITO, a transparent conductive material) to form sensing electrode and scan electrode array on glass surface. The sensing electrodes and the scanning electrodes respectively form a capacitance with ground, which is the so-called self-capacitance, that is, the electrode capacitance to ground. When the fingers touch capacitive screen, the finger capacitance will be added to the screen capacitance, so that the screen capacitance increases. In detecting the touch, the self-capacitance screen sequentially detects the sensing electrode and the scan electrode array. Based on the capacitance change before and after the touch, the coordinates of the sensing electrode and the scan electrode are determined respectively and then combined to become the coordinates of touch point. The scanning manner of the self-capacitance is equivalent to projecting the touch point on the touch screen to the X-axis and Y-axis directions, respectively. Then, the coordinates in the X-axis and Y-axis direction are calculated and combined into the coordinates of the touch point. FIG. 1 shows the theory behind the mutual capacitive touch screen. The manufacturing of mutual capacitance screen is also to form the sensing electrode Rx and scan electrodes Tx. The mutual capacitive screen differs from the self-capacitive screen in that a coupling capacitance CM is formed where the two groups of electrodes intersect. In other words, the two groups of electrodes become the two poles of the coupling capacitance CM. When a finger touches the capacitive screen, the touch affects the coupling between the two electrodes near the touch point, thus changes the value of the coupling capacitance CM between the two electrodes. When detecting the value of mutual capacitance, the sensing electrodes emit excitation signal, and all the scan electrodes receive the signals. As such, the values of capacitances at all the junctions of the sensing electrode and the scan electrodes can be obtained, which is the two-dimensional capacitance of the entire touch screen. According to the information of the change in the two-dimensional capacitance of the touch screen, the coordinates of each touch point can be calculated. As such, multiple touch points on the screen can also be calculated.
In the known mutual capacitive touch screen, one approach is to manufacture the sensing electrodes Rx and scan electrodes Tx with two layers ITO conductive material respectively, and disposed on two non-coplanar parallel planes. The touch screen manufactured by this approach is called the double layer ITO (DITO) mutual capacitive touch screen. This approach requires complex manufacturing process and the yield rate is restricted by the manufacturing process. Another approach is to dispose the sensing electrodes Rx and scan electrodes Tx on the same plane, which is called the single layer ITO (SITO) mutual capacitive touch screen. In known SITO techniques, the sensing electrodes Rx and scanning electrode array Tx are generally disposed in a mutually perpendicular manner, and the two types of electrodes have different shapes so that a visual difference exists between the sensing electrodes Rx and scanning electrode array Tx. As the user can see the outline of the electrodes, this approach does not meet the requirements of the touch screen.